The purpose of this investigation is to explore the intermediary metabolism of purines in the pathogenic leishmaniae and Trypanosoma cruzi. The study will encompass the effects of pyrazolopyrimidine compounds on the extracellular and intracellular forms of these protozoan parasites. This is an extension and amplification of work in progress which has elucidated the salvage pathways of purine metabolism in Leishmania donovani, L. braziliensis, and L. mexicana and documented the effectiveness of allopurinol (4-hydroxypyrazolo-(3,4d) pyrimidine) as antileishmanial agent. The mechanism of action involves the conversion of allopurinol of aminopyrazolopyrimidine nucleotides. T. cruzi possesses similar enzymatic mechanisms. Since this reaction sequence is found only in the pathogenic lieshmaniae and T. cruzi, allopurinol will be used as a biochemical probe to assess purine metabolism in intracellular forms of these protozoans. The investigation will be directed specifically toward intermediary metabolism of purines in the leishmania promastigotes, the use of radiolabeled allopurinol to demonstrate the formation of radiolabeled aminopurinol in the leishmania amastigote, the study of intermediary purine metabloism in T. cruzi, the use of radiolabeled allopurinol to document the formation of radiolabeled aminopurinol nucleotides in the intracellular forms of T. cruzi, and expansion of a murine macrophage tissue culture system which will permit the growth of the intracellular forms of the leishmaniae and T. cruzi.